An agricultural work vehicle which is called ‘tractor’ is structurally similar to general cars, but it has a powerful engine so that it has good traction force and is strong. As a result, the tractor is generally used for cultivation in agricultural work, and so as to perform the cultivation, further, the tractor has various kinds of agricultural work machines detachably attached to the rear side of the body thereof.
So as to improve the efficiencies of the work, the agricultural work vehicle has to have a large gear-shifting range so that a driving speed and a rotational speed of a power take off (which is referred to as ‘PTO’) shaft can be adjusted to optimal speeds according to qualities of soil under the work, and accordingly, the agricultural work vehicle adopts a transmission complicated in structure and having a large gear-shifting range.
FIG. 1 is a sectional view showing a conventional transmission assembly for an agricultural work vehicle.
Referring to FIG. 1, a conventional transmission assembly for an agricultural work vehicle largely includes a transmission 1 and a rear differential 9. The transmission 1 includes a shuttle gear-shifting unit 2 for forward/backward gear-shifting, a main gear-shifting unit 3 and a sub gear-shifting unit 4 for providing a large gear-shifting step range, and a front wheel driving unit 5 for performing bi-speed turn and front wheel driving, and the rear differential 9 is adapted to appropriately distribute the power gear-shifted by the transmission 1 to left and right rear wheels.
The shuttle gear-shifting unit 2 of the transmission 1 is a hydraulic multi-plate clutch for performing selective power connection fey the pressure oil whose flowing is permitted by the lever manipulation of a driver, and the main gear-shifting unit 3 has a synchronized multi-stepped (four step) gear. The sub gear-shifting unit 4 has pairs of gears having different gear ratios moving to left and right sides by means of lever manipulation in such a manner as to be selectively engaged with each other.
The front wheel driving unit 5 is a hydraulic multi-plate clutch in the same manner as the shuttle gear-shifting unit 2. The various components constituting the transmission 1 and the rear differential 6 are located protectedly in a closed space formed by a transmission case 8, and oil as a lubricating agent is filled in the transmission case 8 so as to achieve gentle power transmission between gears, gentle shaft rotation, and friction and abrasion reduction between components.
A reference numeral 7 not explained yet in the figure indicates a PTO gear-shifting unit for taking off the engine power from the vehicle body so that the power generated from the engine is utilized as the power for driving the work vehicle, and a reference numeral 35 indicates a counter shaft having gear-shifting gears rotatable unitarily therewith and freely rotatable therefrom.
FIG. 2 is a sectional view showing the rear differential (rear axle assembly) applied to the conventional transmission assembly.
As shown in FIG. 2, the rear differential 9 largely includes a rear differential case 90 in which a differential 91 is embedded to appropriately distribute the driving power gear-shifted according to driving situations to left and right rear wheels, brake cases 93 assembled with left and right sides to protect brake units 92 spaced apart from each other on both sides of the differential 91, and rear axle cases 96 in which rear axles 95 are insertedly fitted.
A ring gear (bevel driven gear) 910 constituting the differential 91 receives power from a bevel pinion, that is, bevel driving gear (not shown) which outputs finally gear-shifted power through main and sub gear-shifting, thereby rotating the differential 91 and differential axles 94 connected to the differential 91, and accordingly, the rear axles 95 connected to the differential axles 94 rotate, so that the left and right rear wheels rotate with the revolutions finally gear-shifted.
However, the conventional rear differential (rear axle assembly) applied to the agricultural work vehicle largely includes three case components, that is, the rear differential case 90, the brake cases 33, and the rear axle cases 36 coupled to the brake cases 93, thereby causing many disadvantages such as complication in structure, increase in the number of parts, failure in reduction of manufacturing cost, and many difficulties in assembling and so on.